It is known that a singlet oxygen molecule (O2(1Δg)) is generated from the chemical reaction of chlorine gas with a mixed solution of hydrogen peroxide solution (H2O2) and potassium hydroxide (KOH) or sodium hydroxide (NaOH). A chemical oxygen iodine laser (generally called COIL, COIL being an abbreviation for Chemical Oxygen Iodine Laser) which operates as a laser by transferring energy of O2(1Δg) to an iodine atom (I) (i.e. generating I(2P3/2) in an exited state from I(2P1/2) in a ground state) is commonly known as a high energy laser of 1.315 um. Non-Patent literature 1 to 4 explains about the chemical oxygen iodine laser.
Historically, so-called spargers are often used for the above chemical reaction to generate a singlet oxygen generator which is explained in non-Patent literature 5. In the spargers, bubble chlorine gas goes through the mixed solution of H2O2 and (KOH or NaOH) which is called basic hydrogen peroxide (BHP). More particularly, the spargers were mostly used for the COIL from 1977, which is just after the COIL was invented, until the mid-1990s.
While in the 1980s a so called wetted-wall method was used in which chlorine gas contacts a wall which is wetted with BHP solution. Especially, rotating disk generators, which are used in one of the wetted-wall methods, were widely used until the end of 1990s since it is easy to increase a supply amount of the BHP solution by using this method.
After this, so-called jet generators have been used, which have contributed to a high power COIL operation. In the jet generators, BHP solution is injected through nozzles, and is reacted with chlorine gas. Since the total BHP solution surface is large, a large amount of chemical reaction is induced in a short time.
However, the jet generators generate droplets of BHP solution from the injected BHP solution. Since the droplets are transported into a laser cavity, it was pointed out that the droplets negatively affect the laser oscillation. Therefore, so-called aerosol generator has been developed. Since relatively large droplet-generation is suppressed, it is considered to be one of the most advanced methods for generating the singlet oxygen molecule.
One of the reasons for utilizing the energy transfer from the excited O2(1Δg) to iodine as the chemical oxygen Iodine laser is that it is considered that direct lasing from O2(1Δg) is difficult. Actually, there has been no report concerning direct lasing from O2(1Δg). However, there is a report which says weak light was detected in an experiment which aims at achieving the direct lasing of O2(1Δg). In the experiment, a spectrum observation to prove the lasing was not performed. Non-Patent literature 6 is the only a report which says that the direct lasing from O2(1Δg) was successful. According to the Non-Patent literature 5, although the lasing of the oxide laser was confirmed, only a small amount of energy was generated. Since there has been no other report concerning the direct lasing of O2(1Δg) after this experiment, it has been considered that the realization of an oxygen laser is quite difficult.
The reason why the direct O2(1Δg) lasing is difficult is that the quite long spontaneous emission lifetime of O2(1Δg) makes a laser gain, which is inversely proportional to the spontaneous emission lifetime, quite small. However, the small gain does not mean that the lasing is impossible. It just means that lasing is difficult. Therefore it is considered that if the gain length is quite long, lasing is possible. The lasing possibility is shown in the non-Patent literature 7, in which theoretical considerations including experiments are explained along with the purpose of O2(1Δg) lasing.
It is considered that if a large amount of O2(1Δg) is generated in a short time, high pressure O2(1Δg) can fill the inside of the laser cavity in a moment. This gives high gain, and can make the lasing easier. Therefore, it is considered that a pulsed laser operation makes lasing easier. The non-Patent literature 6 and 7 refer to the experiments which aim at conducting a pulsed laser operation.